In an image forming apparatus such as a color printer, image forming conditions (e.g., color registration or image density) may vary in state with time, which can cause errors such as color registration errors or image density errors. In view of this, it has been proposed that the image forming apparatus have a function for adjusting the image forming conditions in order to correct the errors. Frequent execution of the adjustment ensures the quality of images to be formed by the imaging forming apparatus. However, the frequent execution of the adjustment has some disadvantages, such as prolongation of user waiting time or increase in consumption of ink or toner.
In order to prevent excessively frequent execution of the adjustment, some state variations capable of involving a state change in the image forming conditions are detected, and the adjustment is executed when any one of the detected values indicating the state variations (e.g., the number of printed sheets or the elapsed time since the previous execution of adjustment) exceeds a reference value.
This is because color registration errors, due to worn components or vibration during printing operations, may grow to considerable amounts when the number of printed sheets since the previous execution of adjustment has reached a predetermined threshold value, for example. The starting time for adjustment is determined so that the required image quality is maintained, generally assuming the probable maximum errors based on the detected state variations. Consequently, the frequency of execution of the adjustment can be slightly reduced while the required image quality is maintained, compared to periodic execution of the adjustment.
However, there is a need in the art to more accurately evaluate the degree of demand for adjustment of image forming conditions in order to achieve more timely execution of the adjustment.